In an accelerator apparatus, which controls an acceleration state of a vehicle in response to the amount of depression of a pedal that is depressed by a foot of a driver of the vehicle, a rotational angle of the pedal is sensed with a rotational angle sensor. In the rotational angle sensor, each of magnetic flied sensing devices, which are rotatable relative to a magnetic field generating device installed to a shaft, converts a change in a magnetic flux density, into a voltage. In the accelerator apparatus, a valve opening degree of a throttle valve is controlled based on a rotational angle of the pedal, which is computed according to the converted voltage. For example, JP4198544B2 recites an accelerator apparatus, which includes a battery voltage sensing device and a sensor power source voltage sensing device and limits placement of the throttle valve into a full-closing state caused by decreasing of the voltages outputted from the two magnetic field sensing devices at the time of decreasing the electric power supplied to the two magnetic field sensing devices.
In the accelerator apparatus of JP4198544B2, it is determined whether the operation of the accelerator apparatus is normal based on a voltage difference, which is computed based on the two voltages outputted from the two magnetic field sensing devices, respectively. In an abnormal state of this accelerator apparatus where the pedal is further rotated from an accelerator-full-opening time position of the pedal in an accelerator opening direction due to, for example, forced deformation of the pedal, the voltage difference is within a predetermined normal range, in which the operation of the accelerator apparatus is determined to be normal, so that the sensed rotational angle of the pedal is not determined as abnormal.